Furnace pressure regulation



- Sept. 8, 1936.

c. M. TERRY FURNACE PRESSURE REGULATION Filed March 8,

gnumm CHARLES 11. ERR) Patented Sept. 8, 1936 FUBNACE PRESSUREREGULATION Charles M. Terry, Decatur, 111., assignor to A. W.

Cash Company, Decatur, 111., a corporation of Delaware Application Marcha, 1935, Serial No. 10,088

8Clalms.

This invention relates to furnace pressure regulation, and moreparticularly to the regulation of pressure in a furnace having a forceddraft air supply which is started automatically in response to a demandfor heat.

It is common practice to control the pressure in a combustion chamber orfurnace by regulating-the discharge of the gaseous products of com-'bustion from the furnace. This is ordinarily accomplished through themedium of an automatic regulator responsive to variations in furnacepressure and arranged to actuate a damper at the furnace outlet. Theforced draft air supply to such a furnace is sometimes startedautomatically, usually by a thermostatic device or by a deviceresponsive to variations in steam pressure. The sudden inrush of aircauses the furnace pressure to increase, and the automatic regulatorimmediately starts to open the damper, which has remained nearly closedwhile the forced draft was shut down. In many cases the automaticregulator cannot open the damper with sufllcient rapidity to avoid aconsiderable increase in furnace pressure, and asa result flame andsmoke issue into the room from all cracks and openings in the furnacewalls.

It is accordingly the main object of the present invention to overcomethis difficulty and provide simple and reliable means to ensure a freedischarge of gases from the furnace when the forced draft air supply isstarted.

It is a further object of the invention to provide simple and reliablemeans to move the fur-= nace outlet damper automatically'to open position just prior to each automatic starting of the forced draft airsupply.

vention resides in the combination of parts set forth in thespecification and covered by the claims appended hereto.

Referring to the drawing illustrating one embodiment of the invention,and in which like reference numeralsindicate like parts,

The single figure is a diagrammatic elevation, partly in section, of a.forced draft furnace having automatic means for regulating the pressuretherein.

The embodiment illustrated comprises walls It! forming a furnacecombustion chamber ll fired by means of. an underfeed stoker l2 having aretort l4 and tuyere blocks l5. Air is supplied to the space l6 beneaththe retort by means of a forced draft fan l8 driven by a motor IS. Themotor illustrated is an electric motor directly connected to the fan,and it also serves to actuate the stoker l2 through a chain-and-sprocketdrive 20. The heat from the furnace II is utilized to generate steam ina boiler 22 mounted thereabove. The furnace gases flow in contact with 5the boiler heating surfaces and then escape through a gas outlet oruptake 23 to a suitable stack (not shown). The .gas outlet 23 isprovided with an adjustable damper 24 having an operating arm 25.

. 10 The damper 24 is controlled automatically by a suitable regulatorresponsive to variations in the. pressure in the furnace ll.

For'this purpose I preferably utilize an automatic regulator 21 of thetype disclosed in the patent to Temple No. 15 1,992,048 granted February19, 1935. This regulator comprises a pilot valve mechanism 28 suppliedwith a suitable fluid under pressure through a. pipe 28 and connected bytubes 3| to a hydraulic motor 32. This motor 32 is connected to thedamper operating arm 25 by means of a rod 33. The regulator 21 isconnected to the furnace II by means of a pipe 34, so that the furnace.pressure is effective to actuate the regulator. The regulator isadjusted to maintain a furnace pressure slightly below atmosphericpressure, say a negative pressure of one-tenth inch water. column.

The electric motor I9 is connected to a suitable electrical supply 36 bymeans of conductors 31 which lead through an electro-magnetlcallyactuated switch 38. This switch is provided with a holding coil 39, andthe parts are so arranged that upon energization of this coil the switchwill be closed and the motor I 9 will start.

In order to control the rate of steam generation automaticallm'means isprovided for starting and stopping the motor l9 at intervals inaccordance with the demand for steam. For this purpose I have shown apressure-actuated master switch 4| of the well-known mercury tube typeconnected by a pipe 42 to the steam delivery pipe 43 of the boiler 22,and arranged to close at a predetermined minimum steam pressure and openat a predetermined maximum steam pressure. This switch 4| serves tocontrol the supply of electricity from a suitable source 45 to a pair ofpower leads 46 and 41. The source 45 is shown as independent of thesource 36, but it will be understood that this is not necessarily thecase.

It will now be apparent that if the holding coil 39 isconnected'directly across the power leads 46 and 47, as has beencustomary in the past, certain difliculties will arise. With the fan l8shut down, combustion will be very slow, and the regulator 21 will holdthe damper .24 in a nearly closed position to maintain the desiredpressure in the furnace i I. If now the steam pressure dropssufllciently to close the switch 4|, and the fan motor I9 is immediatelystarted, the regulator will be unable to open the damper fast enough toprevent a considerable increase in the furnace pressure, with attendantemission of flame and smoke.

In order to overcome this dimculty I provide means to vent the regulator27 to atmosphere immediately upon closure of the pressure-actuatedswitch ll, and I provide means to interpose a slight time delay betweenclosure of the switch 4| and closure of the switch 38. Since theregulator is adjusted for a slightly negative pressure, it will start toopen the damper 2 immediately after being vented to atmosphere, and thetime delay will allow completion of the opening movement before theforced draft supply is started.

In the preferred construction illustrated, a valve 49 is mounted in thepipe 35 to provide an atmospheric vent 50 controlled by a valve member5|. The valve member normally rests by gravity in a position to closethe vent. The valve member 5| is directly connected to the plunger 53 ofa solenoid 54, the parts being so arranged that upon energization of thesolenoid, the plunger and valve member will be raised and the vent 50opened. It is also desirable to close communication with the furnaw Hupon opening of the vent 50, so as to avoid a rush of air through thevent and into the furnace. For this purpose I provide a partition wall55 which extends acrossthe interior of the valve -38 between the ventand the furnace. This wall is provided with a port 56 located directlyabove the vent to and in a position to be closed by the valve member 5iwhen latter is raised by energization of the solehold 53. It will beseen that this construction provides means whereby the regulator s. ma Lconnected to the furnace it when it is desire to control the furnacepressure, and to the mosphere when it is desired to open 2! fully andobtain high draft in while the forced draft supply is st An automaticswitch mechani m vlded to cooperate with the various ctc. arts ensurethe desired time delay between energize.- tion of the solenoid G6 andclosure of the switch 38. This mechanism comprises a switch connected inseries with the solenoid across the power leads it and d'l, and a switch'3 connected in series with the holdingcoii 31 across the power loads 45and ll. The parts are so arranged that when the switch is closed, theswitch Bil will be open, and vice verse... In the preferred constructionboth the switches and 60 are formed in a single glass tube 622containing a small amount of mercury 2'53. The tube 62 is supported in aclip 65 which is pivotally mounted on a pin 86, suitable stops ti? and33 being provided to limit the pivotal movement the clip. When the cliprests against the stop 3? the mercury 63 will close the switch 59, whenthe clip rests against the stop 68 the mercury will close the switch 66.

In order to actuate the switches 59 30, I provides. link 10 pivoted atits upper end to clip 84 and having a roller ii at its lower end. Acoiled tension spring 12 is connected to link and holds the roller H incontact with the V shaped end of a lever H which is plvotally supportedon a pin 15. The movements of the lever '54 are controlled by means of asolenoid "if; connected across the power leads 56 and 671 and proaooavsoMovement of the lever 1 3 following energization of the solenoid i5 isretarded by a suitable dash pct 83 having a piston 85; connected by apiston rod so to the lever. The piston 89 is formed with ports 92controlled by an annular valve 93 resting on the upper surface of thepiston. A passage 95 connects the space above the piston with the spacetherebeneath, and a manually adjustable valve 95 is provided to controlthe flow in this passage. The dash pot is filled with a suitable liquid,such as oil.

The operation of the invention will now be apparent from the abovedisclosure. During the off period the parts will be in the positionsshown in the drawing, with switches ti, 38 and 238 open, and switch 59closed. The fan i8 and Stoker l2 will be shut down, and the valve member5i will close the vent Elli. Under these conrlitions the regulator 2?will control the position 0; the damper 2d and maintain a pressure inthe furnace it slightly below atmospheric pressure. If now the steampressure drops to a predetermined value, the switch ll will close,energizing the solenoids i l and iii. The solenoid 54 will lift thevalve member 5i, closing port 56 and cpening the vent 5D, wherev son theregulator 27 will start to move the d. KIDS-l 23 toward open position.At the same olenoid 16 will 'lll thereupon slowly raise the collar andturn lever i against resistanceo: the dash time delay which cm beadjusted by r a of the dash pot val 2 3 to reach its 0 Q, i have movedits v feast the roller ll, whereup pull the roller down the other throwthe clip 5 against the lion. This will close the holding coil 39.closing: starting the motor 30, fan is and the same time, the switch [58will be opened, deenergialng the solenoid 6G and dropping the valvemember 58 into position to close the vent Bil. The regulator 2? willthen control the damper i6 and maintain the desired pressure in thefurnace M.

tron, the lever d point slightly e spring it will Upon increase in thesteam press 1 e to a value I switch ll, solenoid l6 dcient to open thend i. s ldin coil 80 will be vie-energized. the switch 38 and shut downthe inc- Ulub ne'er iii and a, and the freely. The regulator 2'17 willcontinue to main tain the desired furnace pressure.

Having thus described my invention, what I claim as new and desire tosome by Letters Patent is:

1. A control for c a the rod 79 and compress .he spring 85, which toallow the forced, draft air supply comprising a regulator normallyresponsive to the furnace pressure and arranged to maintain saidpressure at a value slightly below atmospheric pressure by controllingthe discharge of the gaseous products of combustion from the furnace, adevice to start the forced draft air supply automatically in response toa demand for heat, and means to vent the regulator to atmosphere for ashort time just prior to the starting of the forced draft air supply.

2. A control system for a furnace having a forced draft air supplycomprising a regulator normally responsive to the furnace pressure andarranged tomaintain said pressure at a value slightly below atmosphericpressure by controlling the discharge of the gaseous products ofcombustion from the furnace, means providing a vent through whichatmospheric pressure may be effective on the regulator, a valve membernormally closing the vent, a device to start the forced draft air supplyautomatically in response to a demand for heat, and means to move thevalve member and open the vent for a short time just prior to thestarting of the forced draft air supply.

3. A control system for a furnace having a forced draft air supply and adamper to control the discharge of the gaseous products of combustionfrom the furnace comprising a regulator normally responsive to thefurnace pressure and arranged to maintain said pressure at a valueslightly below atmospheric pressure by controlling the damper, a deviceto start the forced draft air supply automatically in response to ademand for heat, and means to vent the regulator to atmosphere for ashort time just prior to the starting of the forced draft air supply 4.A control system for" a furnace having a forced draft air supplycomprising a regulator normally responsive to the furnace pressure andarranged to maintain said pressure at a value slightly below atmosphericpressure by controlling the discharge of the gaseous products ofcombustion from the furnace, means providing a vent through whichatmospheric pressure may be effective on the regulator, a valve membernormally closingthe vent, means to move thevalve member and open thevent in response to a demand for heat, means to start the forced draftair supply a short time after the vent is opened, and

' means to move the valve member and close the vent when the forceddraft air supply is started.

5. A control-system for a furnace having a forced draft air supplycomprising a regulator normally responsive to the furnace pressure andarranged to maintain said pressure at a value slightly below atmosphericpressure by controlling the discharge of the gaseous products ofcombustion from the furnace, a conduit arranged to transmit the furnacepressureto the regulator,

said conduit having a port therein and an atmospheric vent between theport and the regulator,

a valve normally closing the vent, a device to start the forced draftair supply automatically in response to a demand for heat, and means tomove the valve into a position to open the vent and close the port for ashort time just prior to the starting of the forced draft air supply.

6. A control system for a furnace having a forced draft air supplycomprising a regulator, normally responsive to the furnace pressure andarranged to maintain said pressure-at a value slightly below atmosphericpressure by controlling the discharge of the gaseous products ofcombustion from the furnace, means providing a vent through whichatmospheric pressure may be effective on the regulator, a valve membernormally closing the vent, a solenoid to move the valve through whichatmospheric pressure may be effective on the regulator, a valve membernormally closing the vent, a solenoidto move the valve member and openthe vent, a starting mechanism for the forced draft air supply, a coilto actuate the starting mechanism, two electrical power leads, a deviceto energize the power leads in response to a demand for heat, a switchconnected in series with the solenoid across the powerleads, a switchconnected in series withthe coil across the power leads, a solenoidconnected across the power leads and arranged when energized to open thefirst switch and close the second switch, and meansto' provide a shorttime delay between energization of the last mentioned solenoid andactuation of the switches.

8. A control systemfor a furnace having a forced draft air supplycomprising a regulator normally responsive to the furnace pressure andCly closing the vent, a solenoid to move the valve member and open thevent, a starting mechanism for the forced draft air supply, a coil toactuate the starting mechanism, two electrical power leads, a device toenergize .the power leads in-response to a demand for heat, a pivotallysupported glass tube containing mercury and arranged to provide twoswitches one of which is open when the other is closed and vice versa,means connecting one switch in series with the solenoid across thepower-leads, means connecting the other switch in series with the coilacross the power leads, a solenoid connected across the-power leads andarranged when energized to tip the tube and close the switch which isconnected with the coil and open the other switch, and a dash pot toprovide a short time delay between energization of the last mentionedsolenoid and tipping of the tube. i

' CHARLES M. TERRY.

